Modern petroleum refineries, petrochemical plants, and other facilities, particularly those which use steam boilers are largely automated and operated from a remotely located control center for reasons of both safety and economy. Inherent in this operation is the need to remotely determine when valves have been actuated, and particularly when safety relief valves have been actuated by an unsafe pressure condition. Such information is communicated to the control center by standardized low voltage systems which utilize a transmitter at the remote location.
The first movement of the closure member as the safety valve opens has previously been sensed by either mechanical contact or mercury contact switches mechanically coupled to the moving part of the valve. These devices have been used for many years but have not been wholly satisfactory because they require excessive movement of the valve before opening, thus sometimes failing to detect a partial opening, are intricate in structure in order to achieve the necessary adjustability and sensitivity, have required excessive force to operate which interferes with the normal operation of the valve, and have been subject to damage due to the excessive vibrations inherent in most applications of this type of equipment.